The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 62 708.8, filed on Dec. 23, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a pressing arrangement of a machine for producing a tissue web, having at least one press nip formed between a shoe press unit and an opposing roll, where the shoe press unit includes at least one press shoe lying across from the opposing roll and a flexible, watertight press belt, the opposing roll has a smooth surface, and the tissue web is guided through the press nip along with the press belt and at least one felt and is subsequently removed from the felt and picked up by the smooth surface of the opposing roll. Such a pressing arrangement can be one part of or essentially form the entirety of the pressing arrangement of the tissue machine in question.
2. Discussion of Background Information
In a pressing arrangement of the type mentioned at the outset known from DE 196 54 198 A1 having a drying cylinder forming the opposing roll, the tissue web travels out of the press nip in an approximately tangential direction relative to the surface of the drying cylinder.
The present invention provides a pressing arrangement of the type mentioned at the outset with which a higher dry content of the tissue web leaving the press nip can be achieved and with which a more economic production of tissue is guaranteed.
According to the invention, an angle between the tangent positioned against the opposing roll at the end of the press nip and at least one felt leaving the press nip is greater than or equal to about 10xc2x0, in particular greater than or equal to about 15xc2x0, in particular greater than or equal to about 18xc2x0, and preferably greater than or equal to about 20xc2x0.
Due to this construction, a higher dry content of the tissue web after the press is achieved.
In particular, a shoe press roll having a press jacket forming the press belt, can be provided as a shoe press unit.
Preferably, a drying cylinder and, in particular, a so-called Yankee cylinder, is provided as an opposing roll.
The surface of the press belt can be blind-bored and/or grooved.
More advantageously, the press belt has an open surface xe2x80x9cfxe2x80x9d of f greater than or equal to about 25%.
For an open surface of, e.g., f=36%, of a grooved press belt and/or press jacket at an exit angle of the felt of xcex1=20xc2x0, a 4.5% increase in the dry content can be achieved as compared to the dry content achieved using a conventional suction press roll instead of a shoe press roll.
The pressing arrangement according to the invention may be advantageously used in tissue machines such as, in particular, a suction breast roll former, twin wire former, crescent former, fourdrinier wire former, and/or the like and/or in combination with xe2x80x9cthrough air dryingxe2x80x9d concepts.
The present invention is directed to a pressing arrangement of a machine for producing a web. The pressing arrangement includes a shoe press unit and an opposing roll arranged to form at least one press nip. The shoe press unit includes at least one press shoe arranged opposite the opposing roll and a flexible, liquid-impermeable press belt arranged to be guided over the press shoe. The opposing roll includes a smooth surface. At least one press felt is arranged to be guided through the press nip along with the press belt and the web. The at least one felt is subsequently separated from the web, which is picked up by the smooth surface of the opposing roll, such that the at least one felt is guided out of the press nip at an angle greater than or equal to about 10xc2x0 to a tangent to the opposing roll at an end of the press nip.
In accordance with a feature of the invention, the at least one press felt can be guided at an angle of greater than or equal to about 15xc2x0 to the tangent to the opposing roll at the end of the press nip. Further, the at least one press felt may be guided at an angle of greater than or equal to about 18xc2x0 to the tangent to the opposing roll at the end of the press nip, and preferably, the at least one press felt can be guided at an angle of preferably greater than or equal to about 20xc2x0 to the tangent to the opposing roll at the end of the press nip.
According to another feature of the invention, the web can include a tissue web.
In accordance with still another feature of the present invention, the press unit may include a shoe press roll with a press jacket, and the press jacket can form the press belt.
The opposing roll may include a drying cylinder, and the drying cylinder can include a Yankee roll.
Further, a surface of the press belt may include at least one of blind-bores and grooves. The at least one of the blind-bores and grooves can be arranged such that the surface is greater than or equal to 25% open.
According to a further feature of the instant application, the surface of the press belt may have an open surface of greater than or equal to about 25%.
Moreover, the machine for producing a web can include a tissue machine. Still further, the machine for producing a web can include a suction breast roll former of the tissue machine. Alternatively, the machine for producing a web may include a twin wire former of the tissue machine. The machine for producing a web can also include a crescent former of the tissue machine, or a fourdrinier former of the tissue machine. Also, the pressing arrangement can be utilized in combination with a through air drying device.
According to another feature of the invention, a thin fabric may be arranged between the at least one press felt and the web. The thin fabric can be one of a dewatering wire and an imprinting wire. Further, the thin fabric may have a thickness less than about 2 mm, and advantageously less than about 1 mm.
The present invention is directed to a process for producing a web in an apparatus that includes a shoe press unit and an opposing roll arranged to form at least one press nip, where the shoe press unit includes at least one press shoe arranged opposite the opposing roll and a flexible, liquid-impermeable press belt arranged to be guided over the press shoe and the opposing roll includes a smooth surface, and at least one press felt. The process may include guiding the web, the at least one press felt and the press belt through the at least one press nip, and guiding the at least one press felt from an exit of the press nip an angle greater than or equal to about 10xc2x0 to a tangent to the opposing roll at the exit of the press nip. In this manner, the at least one press felt is separated from the web, which is picked up by the opposing roll.
In accordance with a feature of the present invention, the at least one press felt may be guided from the press nip exit at an angle greater than or equal to about 15xc2x0 to the tangent to the opposing roll at the press nip exit. Further, the at least one press felt can be guided from the press nip exit at an angle greater than or equal to about 18xc2x0 to the tangent to the opposing roll at the press nip exit, and preferably, the at least one press felt may be guided from the press nip exit at an angle greater than or equal to about 20xc2x0 to the tangent to the opposing roll at the press nip exit.
According to still another feature of the invention, the drying cylinder can include a Yankee roll, and the process may further include heating the web in the at least one press nip.
In accordance with yet another feature of the instant invention, a surface of the press belt may have an open surface of greater than or equal to about 25%, and the process can further include carrying away water with the press belt.
In accordance with still yet another feature of the present invention, the apparatus further includes a thin fabric arranged between the web and the felt, and the process can further include deflecting the thin fabric away from the web at an angle less than or equal to the angle of the felt.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.